It is known that, in such propulsive system, generally so-called CROR (for “Contra-Rotating Open Rotor”), each propeller comprises a hub concentrically surrounded by a hub envelope, each hub envelope projecting on either part of the plan of the corresponding propeller. In such propulsive system type, the centre of gravity of each propeller is adapted to be deviated from the axis of rotation thereof, thereby resulting, upon its rotation, in a radial unbalance phenomenon. Now, such unbalance is able to generate mechanical vibrations being able to be transmitted to a piece of equipment—in particular the nacelle of an aircraft receiving passengers—to which the propulsive system is attached, which can be unpleasant for them.
In order to eliminate (or at least to reduce) such possible radial unbalance, it is already known to fit a set of counterweights on locations provided on the propulsive system, in the plan of each propeller, being orthogonal to the axis of rotation thereof. It will be understood that “plan” in this application means the same as “plane,” and these terms are used interchangeably herein. The centre of gravity of each propeller can then be repositioned relative to the axis of rotation thereof by appropriately arranging, on said locations, counterweights, the masses of which are adequately selected taking their locations into account, which can be for example performed upon test phases of the propulsive system, either on the ground, or in flight conditions.
However, such balancing for the propulsive system is frequently found insufficient. Indeed, when the propulsive system is in flight, the propeller blades are subjected to a set of aerodynamic forces, amongst which axial aerodynamic thrust and resistance forces. It results in additional forces and moments occurring, to which said propellers are subjected, thereby unbalancing all the more the propulsive system.
The object of the present invention is to remedy such disadvantage.